According to change of enterprise scale etc., a predetermined database system may be converted to the other database systems. As technology for conversion of the database system, there is technology described in Japanese Unexamined Patent Application No. 2002-351710, for example.
The SQL sentences which can be used for a database system differs for every system as described in the Japanese Unexamined Patent Application. Then, in the system of the Japanese Unexamined Patent Application, smooth conversion of a database system is achieved by cooperating GUI technology and SQL sentence automatic conversion process.
Although the target for conversion in the Japanese Unexamined Patent is the SQL sentence itself, the target for conversion is not only the SQL sentence. Therefore, generally suitable conversion of the database system cannot be performed only by converting the SQL sentence.
For example, the case that the database system to be converted is “Access” (trademark) of Microsoft Corp., and the database system after conversion is similarly SQL Server of Microsoft Corp., will be explained.
In this case, although a view, an in-line table value function, and a stored-procedure are defined as query in the SQL Server, query of “ACCESS” have the same function, but the type in particular is not defined.
Therefore, in case that the database system which is constituted by “Access” is converted to the database system which is constituted by SQL Server, you have to convert each query of “Access” into the query of SQL Server which has a suitable type based on the contents of the query.
Therefore, it is necessary to perform judgment of the suitable type of the query after conversion in the early stage of conversion processing.
However, when determining a suitable type based on the contents of the query, in the case there are six judgment conditions for type determination, it have to perform judgment branch of 64 times. Therefore, there is a disadvantage that the processing cost needed for judgment will become great.